The idea of blocking a firing pin to prevent the discharge of a rotary-bolt firearm when the bolt is in an unlocked position is not new. U.S. Pat. No. 2,685,754 to L. R. Crittendon et al., which has a common assignee with the present application, shows such a block; and this invention is an improvement to that device. In the Crittendon Patent, the travel of the firing pin is limited by its retaining pin, which is mounted in the bolt carrier to extend across a flat on the firing pin. Cam means connecting the bolt with the carrier are arranged to rotate and lock the lugs of the bolt to those of the barrel before the carrier completes its forward stroke, allowing some lost motion at the end of this travel. The dimensions are so selected that until the bolt has first been locked and then the lost-motion portion of the carrier stroke has been at least partially completed, the firing pin is restrained by its retaining pin from protruding from the bolt face far enough to fire a cartridge. On firing, the forward momentum of the firing pin is absorbed in part by impact against its retaining pin. This may sooner or later distort the parts enough to interfere with proper operation of the firearm. In an extreme case, distortion may cause the firing pin to jam with its tip protruding from the bolt face. Further, the block is inoperative if the retaining pin is broken or missing.
Another prior-art design of interest is shown by U.S. Pat. No. 3,397,473 to Browning, in which, in common with the present invention, cam means rotate the bolt as a result of sliding motion of the carrier. However, forward motion of the firing pin relative to the bolt is limited only by its engagement with the bolt, or with a retaining pin mounted in the bolt. Therefore, the firing pin is not positively blocked against protrusion from the bolt face when the bolt is unlocked, but is merely biased rearwardly by the firing pin spring.
Prior-art firing pin blocks for bolt-action firearms are shown in U.S. Pat. No. 2,926,446 to Benson, and U.S. Pat. No. 2,976,637 to Robinson. Benson discloses a bolt-action rifle in which a lug on the firing pin is engageable by a cam on the bolt handle; when the handle is raised to unlock the bolt, the cam retracts the firing pin behind the bolt face. Robinson is an example of a hammerless bolt-action rifle in which a firing pin is cocked rearwardly by a cam on the bolt when its handle is raised, and positively held by the cam in this retracted position until the handle is lowered to lock the bolt.